Cathode ray tube



1965 P. J. MESSINEO ETAL 3,154,737

CATHODE RAY TUBE Filed May 8, 1961 m J? m M WJW m a if GM #1 f i v WQZZM United States Patent 3,164,737 CATHODE RAY TUBE Paul .1. Messineo, Skiilman, and Josef Gross, Princeton, N.J., assignors to Radio Corporation of America, a corporation of Delaware Filed May 8, 1961, Ser. No. $8,431 Claims. (Cl. 313-69) This invention relates to cathode ray tubes for producing images in multiple colors and to electron guns for such tubes. The invention is particularly directed to the electron gun assembly for use in tubes which include a luminescent screen comprising a plurality of superimposed phosphor layers, each of which layers when excited by electrons emits light of a diflerent color from that emitted by the others. Representative screens of this type and their operation are fully disclosed in application Serial No. 108,565 by Dalton H. Pritchard filed May 18, 1961, and entitled Electrical Devices and Methods.

In cathode ray tubes of the type described above, it is known to selectively excite the phosphor layers with electrons to produce luminescence of a given color. The particular phosphor layer or layers excited, and hence, the color of light emitted, is a function of the velocity of the exciting electron beam. By selectively varying the velocity of a single beam or by providing a plurality of different beams of selected velocity and by applying suit able video and chrominance signal information to the beam or beams, a multicolor image can be produced.

It has been proposed to provide a plurality of separate electron guns which can be operated at different voltages relative to the luminescent screen so as to provide a plurality of different velocity electron beams. All of the beams are then deflected by a common deflection means such as an electromagnetic deflection yoke external to the tube to scan the beams in a composite raster or pattern over the luminescent screen. However, since the beams are of diiferent velocities, they will be deflected ditlerent amounts by the common deflection means and thus will result in noncoincident rasters of different sizes on the screen. In order to provide an acceptable composite multicolor picture, the rasters must be coincident and of equal size.

Accordingly, it is an object of this invention to provide a plural beam cathode ray tube of the type described and a method of operating it in which the separate rasters produced by the various electron beams are coincident and of equal size.

It is also an object of this invention to provide electron gun apparatus for producing a plurality of different velocity electron beams which can be scanned by a common deflection field to provide a corresponding plurality of equal size coincident rasters.

The invention is embodied in a cathode ray tube which has a luminescent screen of the type described and which includes three separate electron guns, each of which can be independently electrically energized to provide a different velocity electron beam. The guns are arranged to project their beams through a common deflection field and onto the luminescent screen. At least all but one of the guns are further provided with end electrodes which have different lengths thereof positioned within the deflection field and thus difierentially shield their respective beams from portions of the deflection field. For example, separate tubular shield electrodes of different lengths are attached to the ends of at least all but one of the guns. By virtue of the tubular shields, the beams will be subjected to the common deflection field over respectively different distances of travel through the region of the common deflection field and thus shielded difierent amounts. The lowest velocity beam is shielded 3,164,737 Patented Jan. 5, 1965 ice the greatest amount, i.e., over the greatest distance, the next lowest velocity beam over the next greatest distance, and so on, the highest velocity beam thus being shielded over the shortest distance. Thus, by properly choosing beam velocity and shield lengths substantially equal deflection of all beams, and thus substantially equal size and coincident rasters, can be produced.

In the drawings:

FIG. 1 is a side elevation view in partial section of a cathode ray tube embodying the invention;

FIGS. 2 and 3 are transverse section views of the tube of FIG. l taken, respectively, along lines 2-2 and 33; and

FIG. 4 is a perspective view of a portion of the tube of FIG. 1.

FIG. 1 illustrates a cathode ray tube 8 comprising an evacuated envelope including a neck section 10, a faceplate 12, and an interconnecting funnel section 14. Disposed within the neck 10 is an electron gun apparatus comprising, for example, three electron guns 16, 17, and 18 adapted to project different velocity electron beams through a deflection zone 19 and toward the faceplate 12. The electron guns 16, 17, and 18 are positioned side by side in a triangular arrangement. However, insofar as the practice of this invention is concerned, such a triangular disposition is not necessary; the electron guns may instead be disposed in a planar array.

A luminescent screen 20 on the faceplate 12 comprises three layers 22, 24-, and 26 of different phosphors (one layer for each of the electron guns) which may, for example, comprise, respectively, red, green, and blue light emitting cathode-luminescent materials. The luminescent screen 20 is such that low velocity electrons will excite the red phosphor layer 22 to produce a predominantly red light output; higher velocity electrons will penetrate the red phosphor layer 22 and excite the green phosphor layer 24 to produce a predominantly green light output; and still higher velocity electrons will penetrate both the red and green phosphor layers 22 and 24 and excite the blue phosphor layer 26 to produce a predominantly blue light output. If desired, the screen 20 may include nonluminescent separator layers between the phosphor layers and a metal backing layer on the red phosphor layer 22 to enhance the operational characteristics of the screen.

As an adjunct to the electron tube 10, a magnetic deflection yoke 28 is provided which closely encircles the envelope of the tube. The yoke 28 is adapted to create horizontal and vertical magnetic deflection fields in the deflection zone 19 to cause the three separate beams of the electron guns 16, 17 and 18 to scan a desired raster or pattern on the luminescent screen 20.

Each of the electron guns 16, 17, and 18 comprises a plurality of coaxial tubular electrodes. Each gun includes a tubular cathode 30 having an end wall which is coated with a suitable electron emissive material. Each cathode 30 is insulatingly mounted within a centrally apertured control grid cup 32. Disposed coaxially beyond the control grid cups 32, in the order named, are centrally apertured screen grid cups 34, tubular focusing electrodes 36, and tubular anodes 38.

The anodes 38 are mounted on a cylindrical convergence cage 40 which is electrically common to all three of the electron guns 16, 17, and 18. The convergence cage 40 is closed at each end with end plates 42. The end plates 42 are provided with aligned apertures coaxial with each of the other electrodes of the three electron guns 16, 17, and 18.

The cathodes 349, control grids 32, screen grids 34, and focusing electrodes 36 of the electron guns 16, 17, and 13 are individually connected to dillerent ones of a plurality of leadin conductors 58 which are sealed through the vacuum envelope in a stem base 52. Thu-s, each of these electrodes can be energized independently of the others to provide electron beams of diflerent velocities each focused in the region of the screen 20.

The convergence cage 40 which supports the anodes 38 is provided with a plurality of spring snubbers 54 which bear outwardly against the neck of the envelope.- An electrically conductive coating 56 disposed on the internal surface of the envelope extends over the funnel 14 and into the neck 10 a distance sufficient to make contact with the snubbers 54. The coating 56 also extends into electrical contact with the luminescent screen 20 including the metallic backing layer on the gun side thereof if such coating is provided. Terminal means such as is illustrated schematically by the arrow 58 is provided for applying a suitable electrical potential to the coating electrode 56 for energizing the anodes 38 and the luminescent screen 20.

The electrodes of the electron guns 16, 17, and 18 are maintained in fixed spaced relationship in a well-known manner such as by mounting them on a plurality of glass rods 59 (only one of which is shown) which extend along the guns. Further details of the mounting of the electron guns 16, 17, and 18 have been omitted from the drawing for purposes of clarity.

The three electron beams generated by electron guns 16, 17, and 18 are caused generally to converge when undefiected at a common point near the center of the luminescent screen 20 by mounting each gun at a small angle with respect to the longitudinal axisof the tube 10. The angle which each gun makes with the tube axis is determined by the dimensions of the tube. In cathode ray tubes of the type described having a tube length of about 25 inches, this angle is in the order of 11. FIG. 1 exaggerates the angle between each gun and the tube axis for the purpose of illustration.

In accordance with known color television receiver techniques, dynamic convergence is provided to maintain the beams suitably converged at the screen as they are scanned thereover. As shown in FIG. 2, one representatively suitable dynamic converging means includes a separate pair of pole pieces 60 disposed on opposite sides of each beam Within the convergence cage 40. Associated with each pair of pole pieces 60 is a separate electromagnet 62 disposed. externally of the tube envelope adjacent to the ends of the pole pieces. More sophisticated arrangements, such as those incorporating a pair of electromagnetic windings in place of the single winding 62, are known in the art but for the sake of brevity and clarity are not herein detailed. A Y-shaped magnetic shield 64 is disposed within the convergence cage for shielding each beam from the convergence fields of the other beams.

V Energization of the coils of the electromagnets 62 will impart to the respective electron beams a radial directional component of travel toward or away from the longitudinal axis of the tube 8. A varying current synchronized with, and related to, the amount of scanning deflection of the three beams is applied to each electromagnet 62 to maintain convergence of the three beams at all times during beam'scan in a manner known in the operation of multibeam color kinescopes used in color television receivers. V

Also, in accordance with known techniques all three beams are broughtto a precise static convergence at the center of the luminescent screen 20 by means provided for adjusting the lateral position of one of the electron beams. This is accomplishedby a magnetic field established between a pair of pole pieces 70 and 72 fixed, for instance, to the electron gun 18 on opposite sides of its focusing electrode 36. An electromagnet (not shown) is fixed to the outer surface of the neck 10 to provide a magnetic field between the pole pieces 70 and 72. This field is in a direction normal to the beams.

'scope.

A. direction of the magnetic field provided by the pole pieces 60, and thus permits a lateral adjustment of the position of one of the three electron beams (for example, the beam produced by the electron gun 18) in a direction which is normal to the radial adjustment of position of the beams as provided by the convergence pole pieces 60 when direct current of suitable intensity and polarity is caused to flow in the coils 62. If desired,

7 an arrangement including permanent magnets in addition to the electromagnetic field established between the pole pieces 79 and 72 may be used. Such an arrangement is known in the art.

In one embodiment of this invention, at least two of the three electron guns 16, 17, and 18 further include tubular magnetically permeable shield members 76 and 78 mounted coaxially therewith on the end plate 42 facing the luminescent screen 28. The tubular shield 76 of the gun 16 is'longer than the tubular shield 78 ofv the gun 17 and extends further into the deflection zone 19 toward the luminescent screen 20.

Deflection of an electron beam by a magnetic field is, fora given length, and'a given shape of the magnetic deflection field, a function of the product of the strength of the deflection field and of the time during "which the beam is subjected to the deflection field. The

strength of the field in the region 19 is the same for all three of the beams. The time factor, on the other hand, is inversely proportional to the velocity of the The lower the velocity of a beam, the longer will be its transit time of travel through the field. Thus, by providing the different length shields 76 and 78 and positioning them in the deflection field, the slowest and medium velocity beams can be shielded from the deflection field over a portion of their travel therethrough. The result is that these beams are subjected to the defiection field a shorter period of time than they would be in the absence of the shields '76 and 78. By properly relating the lengths of the shields 76 and 78 to the relative beam velocities and to the shape and length of the magnetic deflection field, the two slower beams can be subjected to the deflection field for specific time durations which will result in their being deflected the same amount as the high'velocity beam. Thus, in the tube 8 wherein the long shield 76 is a part of the electron gun 16, the short shield 78 is a part of the gun 17, and the gun 18 has no shield at all, these guns are operated to respectively produce the slow, medium, and fast velocity beams.

In one example of a tube made and operated according to this invention, the electron guns consist of the gun structure of FIG. 1 wherein the overall length of each gun between remote ends of the control grid cups 32 and the convergence cage 48 is approximately 4% inches. The magnetic deflection yoke 28 may be a standard yoke such as is used with a 21CYP22A type color kine- Shield tube 76 for gun 16 is about three-eighths inch in diameter and about one inch long; shield tube 78 for gun 17 is about three-eighths inch in diameter and about one-half inch long. Both of the shield tubes 76 and 78 are disposed substantially completely within the deflection zone 19 as shown in FIG. '1. One set of suitable operating voltages Which can be applied to such an embodiment of the invention is as follows:

Vol rage Chart Using the aforementioned 3,16 5', voltages, and with both the shields '76 and 78 positioned substantially wholly within the deflection zone 19 as shown in FIG. 1, substantially equal size and coincident rasters on the luminescent screen 2% can be obt ned. If the shape or length or" the deflection field is changed appreciably, or if the relative beam velocities are change appreciably, then it may be necessary to change the length of the shield tubes 76 and 73 in order to produce th desired raster coincidence.

In accordance with commercial television standards, the horizontal deflection sweep frequency is approximately 16,050 cycles per second and the vertical deflection sweep frequency is approximately 60 cycles per second. Where the tube 8 is intended for commercial television applications, the shields 7d and 73 should therefore be such as to provide approximately the some degree oi magnetic shielding for both these frequencies. The shie ds 75 and 78 should therefore be fabricated from a material, or a composite structure (PEG. 4), which has substantially equal shielding properties (magnetic permeability) for both these two frequencies. As shown in FIG. 4, in one composite structure which has proved suitable, the shield tube 76 comprises outer and inner concentric tubes dd and 32 which are sized to fit snugly together. Similarly, the shield tube 78 comprises outer and inner tubes 84 and In the case of each or" the shield tubes 76 and '78 their concentric tubular elements are such as to compositely exhibit the desired permeability properties. One example of two such suitable materials are alloys sold commercially and designated as Netic and Conetic alloys. Certain known ferrites, such as those used as cores for television deflection yokes, which have substantially equal shielding properties for both the vertical and horizontal sweep frequencies used in commercial television, can also be use The invention has been described in terms or" specific examples and embodiments. However, various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the following claims.

Unless otherwise indicated in the claims, the method steps recited therein need not be carried out in the order named.

What is claimed is:

1. A cathode ray tube comprising an envelope, 2. luminescent screen in said envelope, said screen including a plurality of different color light emitting phosphors, and a plurality of electron guns arranges side by side within said envelope adapted to project difierent velocity electron beams through a common deflection zone toward said screen, at least all but one of said guns having difierent length portions thereof positioned Within said deflection zone.

2. A cathode ray tube comprising an envelope, a luminescent screen in said envelope, said screen including a'plurality of different color light emitting phosphors, and a plurality of electron guns arranged side by side within said envelope adapted to project different velocity electron beams through a common deflection zone and onto said screen, at least all but one of said guns each having associated therewith a beam sh elding member extending along the beam path of its respective gun in said deflection zone, said shielding m mbers having diferent length portions thereof positioned within said deflection zone.

3. A cathode ray tube comprising an envelope, at luminescent screen in said envelope, said screen including a plurality of different color light emitting phosphors, and a plurality of electron guns arranged side by side within said envelope adapted to project different velocity electron beams through a common deflection zone and onto said screen, at least all but one of said guns having ditlerent length beam shielding members positioned in said deflection zone.

4. A cathode ray tube comprising a plurality of electron guns disposed side by side and adapted to project differout velocity electron beams through a common deflection held, a sescent screen beyond said field from said guns in the path of said beams and responsive to said beams to produce light of different colors, the ends of said electron guns adjacent said screen being differentially om said screen, the respective beams of said guns ected to said common deflection field over different distances of beam travel.

" A cat ray tube comprising an envelope, a

J. node nescex: screen disposed on a portion of the internal I .acc or" said envelope, said luminescent screen includa plurality of phosphors which upon electron excitaependent upon the velocity of the exciting electrons, a plurality of electron guns within said envelope whichare adapted to project dift'erent velocity electron beams toward aid screen, and an electrorn .etic deflection zone between said guns and said screen in the paths of said beams, said guns including a plurality of substantially identical coaxially arranged electrodes a first tubular magnetically permeable beam shield surrounding and extending along the beam path of one of said guns and having a given length thereof positioned in said deflection zone, a second tubular magnetically permeable beam shield surrounding and extending along the beam path of another of said guns and having a len th thereof greater than said given length positioned in said deflection zone.

6. A cathode ray tube comprising an envelope, and within said envelope a luminescent screen, and apparatus for generating and d' ting a plurality of separate electron beanis having diiterent velocities toward said screen, said apparatus including a plurality of elongated electron guns disposed side by side along a longitudinal axis, the adjacent ends of said guns closest to said screen being spaced from each other along the longitudinal axis.

7. A cathode ray tube comprising an envelope, at luminescent screen within said envelope, said screen including a plurality of different phosphors which upon electron excitation emit light whose color is dependent upon the velocity of the exciting electrons, and apparatus within said envelope for generating a plurality of separate electron beams comprising a plurality of elongated electron guns each including a plurality of coaxially arranged electrodes, said guns being disposed side by side, the end electrodes at one end of said apparatus of at least all but one of said guns including longitudinally extending portions of magnetically permeable material, said portions being of different lengths for different ones of said guns.

8. A cathode ray tube comprising a'lu nescent screen and apparatus for projecting three separate electron beams along three separate beam paths and upon said screen, said apparatus comprising three electron guns disposed side by side, and two tubular magnetic shields or" different lengths mounted on one end of said apparatus, each of said tubular magnetic shields surrounding a different one of said beam paths.

9. A cathode ray tube comprising a phosphor screen and apparatus for projecting three separate electron beams upon said screen, said apparatus comprising three electron guns disposed side by side, two of said guns having ran LVV tubular magnetic shields at one end of said apparatus,-

said tubular magnetic shields being of diilerent lengths.

It). A cathode ray tube comprising a luminescent screen, a deflection zone spaced from said screen in which a deflection field can be-estaolished, means for projecting a plurality of separate electron beams through said zone and onto said screen, and means for shielding at least all but one of said beams different amounts from said deflection field within said zone.

References fitted in the file of this patent UNITED STATES PATENTS 2,727,828 Law Dec. 20, 1955 2,898,491 Pearce Aug. 4, 1959 

5. A CATHODE RAY TUBE COMPRISING AN ENVELOPE, A LUMINESCENT SCREEN DISPOSED ON A PORTION OF THE INTERNAL SURFACE OF SAID ENVELOPE, SAID LUMINSECENT SCREEN INCLUDING A PLURALITY OF PHOSPHORS WHICH UPON ELECTRON EXCITATION EMIT LIGHT WHOSE COLOR IS DEPENDENT UPON THE VELOCITY OF THE EXCITING ELECTRONS, A PLURALITY OF ELECTRON GUNS WITHIN SAID ENVELOPE WHICH ARE ADAPTED TO PROJECT DIFFERENT VELOCITY ELECTRON BEAMS TOWARD SAID SCREEN, AND AN ELECTROMAGNETIC DEFLECTION ZONE BETWEEN SAID GUNS AND SAID SCREEN IN THE PATHS OF SAID BEAMS, SAID GUNS INCLUDING A PLURALITY OF SUBSTANTIALLY IDENTICAL COAXIALLY ARRANGED ELECTRODES, A FIRST TUBULAR MAGNETICALLY PERMEABLE BEAM SHIELD SURROUNDING AND EXTENDING ALONG THE BEAM PATH OF ONE OF SAID GUNS AND HAVING A GIVEN LENGTH THEREOF POSITIONED IN SAID DEFLECTION ZONE, A SECOND TUBULAR MAGNETICALLY PERMEABLE BEAM SHIELD SURROUNDING AND EXTENDING ALONG THE BEAM PATH OF ANOTHER OF SAID GUNS AND HAVING A LENGTH THEREOF GREATER THAN SAID GIVEN LENGTH POSITIONED IN SAID DEFLECTION ZONE. 